12 research outputs found
Cosmological mass limits on neutrinos, axions, and other light particles
The small-scale power spectrum of the cosmological matter distribution
together with other cosmological data provides a sensitive measure of the hot
dark matter fraction, leading to restrictive neutrino mass limits. We extend
this argument to generic cases of low-mass thermal relics. We vary the cosmic
epoch of thermal decoupling, the radiation content of the universe, and the new
particle's spin degrees of freedom. Our treatment covers various scenarios of
active plus sterile neutrinos or axion-like particles. For three degenerate
massive neutrinos, we reproduce the well-known limit of m_nu < 0.34 eV. In a
3+1 scenario of 3 massless and 1 fully thermalized sterile neutrino we find
m_nu < 1.0 eV. Thermally produced QCD axions must obey m_a < 3.0 eV,
superseding limits from a direct telescope search, but leaving room for solar
eV-mass axions to be discovered by the CAST experiment.Comment: 15 pages, 6 figures, matches version in JCA
Search for solar axion emission from 7Li and D(p,gamma)3He nuclear decays with the CAST gamma-ray calorimeter
We present the results of a search for a high-energy axion emission signal
from 7Li (0.478 MeV) and D(p,gamma)3He (5.5 MeV) nuclear transitions using a
low-background gamma-ray calorimeter during Phase I of the CAST experiment.
These so-called "hadronic axions" could provide a solution to the long-standing
strong-CP problem and can be emitted from the solar core from nuclear M1
transitions. This is the first such search for high-energy pseudoscalar bosons
with couplings to nucleons conducted using a helioscope approach. No excess
signal above background was found.Comment: 20 pages, 8 figures, final version to be published in JCA
Probing eV-scale axions with CAST
We have searched for solar axions or other pseudoscalar particles that couple
to two photons by using the CERN Axion Solar Telescope (CAST) setup. Whereas we
previously have reported results from CAST with evacuated magnet bores (Phase
I), setting limits on lower mass axions, here we report results from CAST where
the magnet bores were filled with \hefour gas (Phase II) of variable pressure.
The introduction of gas generated a refractive photon mass , thereby
achieving the maximum possible conversion rate for those axion masses \ma that
match . With 160 different pressure settings we have scanned \ma up
to about 0.4 eV, taking approximately 2 h of data for each setting. From the
absence of excess X-rays when the magnet was pointing to the Sun, we set a
typical upper limit on the axion-photon coupling of \gag\lesssim 2.17\times
10^{-10} {\rm GeV}^{-1} at 95% CL for \ma \lesssim 0.4 eV, the exact result
depending on the pressure setting. The excluded parameter range covers
realistic axion models with a Peccei-Quinn scale in the neighborhood of GeV. Currently in the second part of CAST Phase II, we are
searching for axions with masses up to about 1.2 eV using \hethree as a buffer
gas.Comment: 18 pages, 7 figures. Revised version of the paper after referee's
comments. Main changes on the gas sectio
New CAST limit on the axion-photon interaction
Hypothetical low-mass particles, such as axions, provide a compelling explanation for the dark matter in the universe. Such particles are expected to emerge abundantly from the hot interior of stars. To test this prediction, the CERN Axion Solar Telescope (CAST) uses a 9 T refurbished Large Hadron Collider test magnet directed towards the Sun. In the strong magnetic field, solar axions can be converted to X-ray photons which can be recorded by X-ray detectors. In the 2013-2015 run, thanks to low-background detectors and a new X-ray telescope, the signal-to-noise ratio was increased by about a factor of three. Here, we report the best limit on the axion-photon coupling strength (0.66 × 10 -10 GeV -1 at 95% confidence level) set by CAST, which now reaches similar levels to the most restrictive astrophysical bounds
Search for 14.4 keV solar axions emitted in the M1-transition of 57Fe nuclei with CAST
23 pages, 5 figures. Revised version of the paper after referee's comments. Main changes in the Measurement and data analysis sectionWe have searched for 14.4 keV solar axions or more general axion-like particles (ALPs), that may be emitted in the M1 nuclear transition of 57Fe, by using the axion-to-photon conversion in the CERN Axion Solar Telescope (CAST) with evacuated magnet bores (Phase I). From the absence of excess of the monoenergetic X-rays when the magnet was pointing to the Sun, we set model-independent constraints on the coupling constants of pseudoscalar particles that couple to two photons and to a nucleon g_{a\gamma} |-1.19 g_{aN}^{0}+g_{aN}^{3}|<1.36\times 10^{-16} GeV^{-1} for m_{a}<0.03 eV at the 95% confidence level
CAST: Status and latest results
In July 2011, CAST finished the data-taking of its nominal programme, having scanned axion masses up to ~1.18 eV/c**2. Here we present the first results of the data taken in 2008, first year of the last data-taking campaign when He was used inside the magnet bores. No excess of signal over background has been recorded, and an upper limit has been set to the axion-to-photon coupling to 2.3*10**-10 GeV**-1 for axion masses between 0.39 and 0.64 eV. CAST remains the most sensitive axion helioscope and for the first time crosses the benchmark line of the KSVZ model at the upper end of the spectrum
CAST: Status and latest results
In July 2011, CAST finished the data-taking of its nominal programme, having scanned axion masses up to ~1.18 eV/c**2. Here we present the first results of the data taken in 2008, first year of the last data-taking campaign when He was used inside the magnet bores. No excess of signal over background has been recorded, and an upper limit has been set to the axion-to-photon coupling to 2.3*10**-10 GeV**-1 for axion masses between 0.39 and 0.64 eV. CAST remains the most sensitive axion helioscope and for the first time crosses the benchmark line of the KSVZ model at the upper end of the spectrum